1. Field of the Invention
The present invention relates to an apparatus for providing an omnidirectional stereo image needed to infer three-dimensional (3D) information using a single camera, and more particularly, to an apparatus for providing an omnidirectional stereo image with a single camera, which provides a wide stereo baseline, decreases its size, and facilitates correspondence search in a stereo image.
2. Description of the Related Art
Stereo vision systems using a camera are used to infer three-dimensional (3D) information from two images. In particular, omnidirectional stereo systems provide 3D information on a 360-degree panorama. Such systems can be used in the field of 3D figure measurement, virtual reality, environment recognition of intelligent robots, monitoring and surveillance systems, military detection systems, etc.
In omnidirectional stereo systems, 3D recovery is accomplished by identifying parallax between two panoramic images obtained at two different viewpoints. The two omnidirectional images can be obtained using two cameras or a single camera and mirrors. When two cameras are used, an error may occur during 3D recovery due to differences in physical characteristics, such as a difference in focal length and misalignment of imaging elements like a charge-coupled device (CCD) and a mirror, between the two camera systems. Accordingly, using a single camera stereo system is known as more effective in various terms.
To easily implement a stereo vision system using a mirror, the shape of the mirror and a relative positional relationship between the mirror and a camera should satisfy a single viewpoint constraint. When this condition is not satisfied, it becomes complicated to extract 3D information from two images. In particular, a plane mirror, an ellipsoidal mirror, a hyperboloidal mirror, and a paraboloidal mirror can satisfy the condition of a single viewpoint constraint and support an omnidirectional system.
FIG. 1 is a conceptual diagram of a system using a hyperboloidal mirror 100 among single-camera omnidirectional mono systems satisfying a single viewpoint. An image of a 3D-space object 110 reflected by the hyperboloidal mirror 100 is projected on an image plane 130 of, for example, a CCD via an effective pinhole 120 of a camera. The image reflected by the hyperboloidal mirror 100 is the same as an image viewed from an effective viewpoint 140.
Meanwhile, conventional single-camera omnidirectional stereo systems are implemented by placing a double-lobed mirror in front of a camera. However, a distance between effective viewpoints in the mirror is very short, and therefore, a depth resolution is very low. Moreover, an apparatus such as a robot requiring a single-camera omnidirectional stereo system is demanded to be small. Accordingly, a single-camera omnidirectional stereo system suitable to compactness is desired. In addition, since two images obtained in a conventional single-camera omnidirectional stereo system have a resolution difference between corresponding points, ability to find corresponding points in the two images may be decreased when the resolution of the obtained images is low. Therefore, a process of compensating for a resolution difference between the two images is desired.